Changes in tissue calcium and phosphorus content and plasma concentrations of parathyroid hormone and calcitonin after long-term magnesium deficiency in rats.

OBJECTIVE: The present study was undertaken to investigate the effect of dietary magnesium (Mg) deficiency on plasma levels of parathyroid hormone (PTH) and calcitonin (CT), and the changes in tissue calcium (Ca) and phosphorus (P) content.
METHODS: Wistar rats were fed an Mg-deficient diet. Plasma levels of PTH and CT, and Ca and P content in plasma, whole blood, skeletal muscle, heart, kidney, femoral bone and brain, were determined after 7, 35, 42, 49, 56, 63 and 70 days.
RESULTS: Mg deficiency significantly increased plasma levels of ionic Ca after 1 week of deficiency, and significantly increased total Ca in plasma and whole blood after 5 weeks. Whole blood and plasma levels of P decreased significantly after 8 and 5 weeks, respectively, in comparison with values obtained in pair-fed control rats. Plasma levels of CT were not modified by hypercalcemia and hypomagnesemia. Plasma PTH decreased significantly during the first 3 weeks, then recovered gradually, reaching control values in week 7 and remaining stable thereafter, despite elevated levels of ionic Ca. The Mg-deficient diet led to calcification in skeletal muscle, heart, kidney and femur, detectable as early as week 5. However, P content increased only in kidney after 1 week, decreased in heart and femur after 5 weeks, and did not change in muscle. The Mg-deficient diet did not significantly modify Ca or P content in brain.
CONCLUSION: Mg deficiency led to tissue calcification and decreased P levels in blood, heart, and femur. These changes did not affect CT secretion. PTH appeared to be more closely related with hypomagnesemia than with hypercalcemia.